Zirconia (zirconium oxide) films, which have characteristics for example of their high heat and corrosion resistance, low thermal and electrical conductivity, have been used as heat-resistant protective films, corrosion-resistant protective films, optical thin films and others. These zirconia films have been produced, for example, by a sol-gel method, a thermal chemical vapor deposition (CVD) method, a sputtering method, or a thermal spreading method, but these deposition methods have some problems, such as deposition rate, deposition condition and film quality, to be improved.
An aerosol gas deposition method is a deposition method of converting raw material fine particles (aerosol raw material) placed in an aerosol-generating container to aerosol by agitation with a gas, conveying the aerosol by the gas stream generated by the pressure difference between the aerosol-generating container and the deposition chamber and thus, making it collide and deposit on a substrate. In the method, a film is formed, as the kinetic energy of the raw material fine particles accelerated to high speed is locally converted to heat energy. Since the substrate heating occurs only locally, the substrate is hardly affected by the heat (normal-temperature deposition) and the deposition rate is higher than that of other deposition methods. For that reason, it can generally give a film having high-density, high-adhesiveness.
For example, the methods described in Patent Documents 1 and 2 are known as the aerosol gas deposition methods using zirconia fine particles as raw material.
Patent Document 1 discloses a “method for forming a brittle material fine particle deposited film at low temperature,” which forms a thin film of a brittle material by an aerosol gas deposition method from brittle material fine particles containing zirconia fine particles as raw material. It is possible according to the method to form a dense and highly adhesive film by using fine particles in the non-spherical indefinite shape as aerosol raw material, because the impact force concentrates on the projections of the fine particles.
Patent Document 2 discloses a “tool material for baking ceramics for electronic parts,” which forms a zirconia-containing surface layer by the aerosol deposition method. It is possible according to the method to prevent separation of a zirconia-containing surface layer from its substrate, by forming an intermediate layer having a linear thermal expansion coefficient between those of the substrate and zirconia on the substrate.
Patent Document 1: Japanese Patent Application Laid-open No. 2003-73855 (paragraph [0010] and FIG. 1)
Patent Document 2: Japanese Patent Application Laid-open No. 2008-137860 (paragraph [0021])